PlaneShift October, 2008

Transcription

1 PlaneShift October, 2008

2 What is PlaneShift MMORPG Like EverQuest or World of Warcraft Extremely ambitious project Free to Play All code under GPL All content under PlaneShift license

3 Made by Amateurs Project started in 2000, by Luca Pancallo in Italy Volunteer project with many contributors 62 coders have directly committed code in the project (22 have over 100 commits) Dozens have submitted patches without direct write access as well. Dozens more have worked on other subteams Relatively large project About 400K lines of C++ in the core applications, in about 1200 classes Uses Crystal Space opengl library, which is >1 million lines of code itself Uses mysql database. >70 tables and >5GB of data 560,000 registered players have tried it, with essentially zero PR. But average concurrently online is only x7.

4 MMO s are complex Normal open source team structure Coding team QA team if you re really organized

5 MMO s are complex PS team structure 2d (concept art, textures) 3d (world/terrain, items, monsters, characters, animation) Sound (effects, background music) Rules (item stats, item definitions, player stats, balancing, progression) Settings (names, npc definitions, quests, histories, books, spells) Web development (game content management) Engine (coding) + QA team Key learning point for me on the project: The content is much more difficult, time-consuming and costly than the engine.

6 Server Unique Design Constraints No money = donated hardware Everything runs on 1 box right now If we move to multiple boxes, they will almost certainly not be colocated = High latency No money = volunteer development team High turnover on a large project Learning curve is a major issue Modularity of design is critical

7 So let s see it

8 Server Design

9 Overview Core of server is an event dispatcher Events can be: Network messages Time triggered messages Intra-server messages No distinction is made internally between these other than queue priority Basic Producer/Consumer threading model for networking vs worker threads. Publish/Subscribe Architecture allows for managers to act like plugins, each specializing in a certain class of events.

10 Benefits of Manager model Classes defined along functional game lines Combat, Spells, Chat, Login all in distinct sources Easy to find code that handles a feature of interest Lower learning curve Get comfortable with a single source file before moving on to others Some never move on, but become the deep maintainers of a certain manager Easy to bolt in new functionality One more manager has no effect on performance or on other managers

11 Manager model in PS

12 Networking / Entity Management

13 Base networking UDP based TCP can result in higher latency due to guarantees on ordering of packets Two priority levels of messages Guaranteed delivery (High) Non-guaranteed delivery (Low) We need a third priority Guaranteed order (Highest) On the to-do list but not done yet Everything is packed pretty tightly byte by byte, and endian correct #1 limiting factor on server capacity is bandwidth consumption Not CPU Not Memory

14 Entity Management Server maintains all entities in-game An entity is any object added after the fact to the maps Characters, monsters, npcs, items dropped by players Each client gets a small subset of these entities As a result, entities are constantly being created and destroyed on each client The server maintains a Proximity List for each client, which holds all relevant entities for that client Prox Lists determine what is visible to each client, which means it determines what updates are relevant to each client also

15 Proximity Lists Diagram A B C D E F G H I J K L M N O P Player F can see himself and 5 other characters Player H can see himself and 6 other characters

16 Proximity Lists Relevance is determined by: Within a threshold distance to the player visible to the player (complex) Within the same instance (or compatible instance) to the player Benefits Better for security (see future slides) Minimizes bandwidth to relevant bandwidth Very easy construct for Managers to use with broadcasting (multicasting) Costs Server spends a lot of time maintaining and updating prox lists

17 Proximity Lists Diagram A B C D E F G H I J K L M N O P

18 Scripting in the Server The game server uses several types of home-made scripting to implement gameplay rather than C++ code. Benefits Possible for non-programmers to produce (Rules, Settings, 2d) Proprietary content not subject to GPL (i.e. secret) Engine team concentrates on extending the scripting languages rather than coding new features directly Meta programming is much more efficient in developer time Costs Complexity of meta code increases learning curve for programmers

19 Math Scripts "Calculate Repair Time" Difficulty = Object:SalePrice/100; Factor = Worker:getSkillValue(Object:RequiredRepairSkill) / (Object:SalePrice/20); Result = Difficulty / Factor; "Calculate Repair Result" Factor = Worker:getSkillValue(Object:RequiredRepairSkill) / (Object:SalePrice/20); Result = ((Object:SalePrice/25) * Factor) * (rnd(1)+0.5); Highlights Precompiled to p-code on server startup Dynamic binding to objects like Object and Worker above Any C++ class can be bound if it implements iscriptable

20 Progression Scripts "DamageHP" <evt> <hp aim="target" value="-param0" /> <msg aim="target" text="you lost $Param0 hitpoints."/> <msg aim="actor" text="you hit $Target for $Param0 hitpoints."/> </evt> Highlights Loaded and compiled to virtual function calls (each operation is a mini-class) Scriptable by Rules team Value attribute can be any single line mathscript.

21 Quest Scripts Quest: "Male Enki Alina Quest" P: Greetings Marth: Hail! Would you like to earn a little money? P: No P: Yes M: Well ok then. Have a good day. M: My daughter Alina ran off with the smith and I fear they are up to no good. If you can find out if he really loves her, I'll pay you. Can you do this for me? P: No P: Yes M: Fair enough. I guess I'll just try to find someone else. M: Last time I caught them upstairs above the blacksmith shop. Please hurry up and ask her! Assign Quest. <snip> P: Greetings Marth: Oh I'm so glad you are back. Did you find him? Does he love her?{him:smith,her:alina} P: * P: Smith says Smith does. Smith love Alina. M: That isn't what Thalia told me 5 minutes ago. You're just faking to get the money! Go away! M: Ah! Thank heavens. Perhaps now they will get married! Thanks for your help! Give 25 tria.

22 NPC Management

23 NPC AI is hard to scale We have a monolithic server today 100 concurrent players takes <5% CPU We can scale up with players fairly far before machine capacity of the core server is an issue. AI is computationally expensive The smarter the monsters, the more expensive AI techniques evolve constantly (and get more expensive) Deep experts exist who may contribute to the game someday AI doesn t belong in the same process, or on the same machine as the server

24 Superclient Architecture psserver NpcManager psclient psclient psclient psclient psclient psclient npcclient npcclient npcclient

25 Superclient Concepts Separate process Connects to server over the network Uses same protocols as client for some things Uses additional special messaging for bulk information transfer NpcManager class on server Handles these special messages, and unrolls them for the rest of the server, republishing them.

26 Superclient Benefits Simplicity in server/client NpcManager emulation layer means there is no distinction between human and automated players in almost the entire server. There is no distinction on a client machine between an NPC and a remote player. Scalability Net connected separate process means the process could be on its own machine. Connecting as a client means that multiple superclients can be connected concurrently. Future expansion No limitations on AI techniques used as long as net protocol is followed by each superclient.

27 How we do NPC AI Artificial Stupidity Monsters don t need much intelligence to be challenging to players (Pac-Man) Emphasis on CPU efficiency and flexibility 1 Superclient controls approximately 300 mobile npcs with <10% cpu today

28 AI Scripting Model - NPCTypes NPCs divided into types or classes All scripting is done at the type level Types consist of Set of Behaviors Set of Reactions to Perceptions Perceptions sent by the game server Perceptions generated internally by the npcclient Inheritance structure for npc types Behavior/Reaction overloading Loose structure enables very flexible scripting and potentially emergent behavior Very hard to debug and maintain

29 AI Scripting Model NPC s Each NPC in the game maintains Priority queue of behaviors in its NPCType, prioritized by need to perform the behavior Hate list of known players who have hurt or helped the NPC NPC runs the script for the behavior with highest need Reactions to perceptions only affect needs and hate. If the need gets high enough, the current behavior is interrupted and replaced with a new behavior. Hate affects targeting in attacks, mostly.

30 AI Scripting Example <npctype name="fighter"> <behavior name="do nothing"> <wait duration="1" anim="stand" /> </behavior> <behavior name="turn" completion_decay="-1"> <rotate type="random" min="90" max="270" anim="walk" ang_vel="30" /> <move vel="2" anim="walk" duration="1.0"/> </behavior> <behavior name="fight"> <locate obj="target" range="50"/> <rotate type="locatedest" anim="walk" ang_vel="120" /> <melee seek_range="50" melee_range="3" /> </behavior> <behavior name="chase" completion_decay="100"> <chase type="target" anim="run" vel="5" /> </behavior> <react event="collision" behavior="turn" /> <react event="out of bounds" behavior="turn" /> <react event="attack" behavior="fight" /> <react event="damage" behavior="fight" delta="20" weight="1" /> <react event="target out of range" behavior="chase" /> <react event="death" behavior="fight" delta="0" /> </npctype>

31 Game Security in Open Source

32 Security Problems with Open Source Hacked clients are trivial Speed/Teleport/Anti-gravity mods Visibility mods Bots and Macroing Collision detection hacks Map hacks Item art hacks Texture mods

33 How to combat these? No defense, low impact Texture mods: They are fun to look at but only visible to the player with the mods Item art hacks: Tight prox list radius on critical small items minimizes impact High impact, Easy defense Visibility mods: Use of prox lists gives us tight control over what is available for the cheater to see Speed/Teleport mods: Server can compare before and after positions and kick out cheaters

34 High impact, Hard defense Bots and Macroing Extremely hard to detect automatically PS is focusing on making repetitive activities less valuable to the player, so diminishing returns makes automation less valuable Collision detection & Map hacks Very expensive in CPU and RAM to monitor on the server centrally. Roadmap is to use a superclient type approach and have a separate process connect to the server to watch for cheaters, focusing on individuals at random intervals.

35 Follow up Main game website Project Director is Luca Pancallo Keith Fulton Come help the team if you like free games and you have a lot of free time!